Heretofore, to reduce noise from an engine of an automobile and others which are noise generation sources, various sound proof materials have been suggested. For example, the present applicant has suggested a sound proof cover which comprises a sound absorbing material arranged so as to face sound sources, an air-impermeable soft sound insulating layer laminated on the sound absorbing material, and a soft cover which forms an air layer between the soft cover and the soft sound insulating layer, whereby, in the sound proof cover, the air layer is hermetically sealed (see Patent Document 1).